This invention is generally directed to processes for the preparation of superconductors, and more specifically the present invention is directed to processes for preparing certain high temperature copper oxide superconductors. Thus, in accordance with the simple, economical process of the present invention there can be prepared superconductors of, for example, the formula YBa.sub.2 Cu.sub.3 O.sub.7-x, wherein x is close to zero, by the reaction of copper nitride, an oxidizing component such as barium peroxide, and a component of the formula Y.sub.2 O.sub.3 wherein y is yttrium. One specific embodiment of the present invention comprises the reaction of Y.sub.2 O.sub.3, barium peroxide, and copper nitride in the presence of oxygen, which reaction is generally accomplished at high temperatures of from about 900.degree. C. to about 975.degree. C.Z, followed by allowing the mixture to cool. With the process of the present invention, there is provided a superconductor of high purity wherein only a single heating step is needed, and morever the process of the present invention is more economical from, for example, a cost standpoint than prior art processes. Accordingly, with the process of the present invention a simple economical method for the synthesis of copper oxide superconductors in a purity of from about 60 to about 95 percent or greater is provided; for example, only about one half of the energy is utilized and the processing time, especially the heating period, is reduced in comparison to many prior art processes. Also, the superconductors of the present invention have know uses equivalent to those of conventional Type 2 superconductors, including their selection for electrical motors, reference C&EN, Jan. 18, 1988, page 23.
Processes for the preparation of superconductors are known. Thus, for example, it is known that copper oxide superconductors can be prepared by high temperature, above 900.degree. C., ceramic methods. In the aforementioned processes, barium carbonate, Y.sub.2 O.sub.3, and copper oxide are admixed, and ground with a mortar and pestle; and subsequently, the resulting product is pressed into pellets. Thereafter, the products are fired in an oven at about 950.degree. C. for about 10 hours. The pellet product after cooling are ground, and pressed a second time, and thereafter sintered at 950.degree. C. for in excess of 10 hours. The resulting material evidences a variety of superconducting properties such as zero dc resistance and the Meissner effect. Often the material is multiphased with undesirable nonsuperconducting phases diluting the superconductor phase. Thus, the copper oxide superconductor resulting of the formula illustrated herein may contain therein impurities such as nonsuperconducting phases, reference for example the Japanese Journal Of Applied Physics, Volume 26, No. 5, May of 1987. For example, one specific contaminant present in the aforementioned superconductors is believed to be the green compound Y.sub.2 BaCuO.sub.5, which in of itself does not function as a superconductor. Generally, this contaminant results from the reactants selected, or utilizing the incorrect stoichiometric reactant amounts in the initial reaction mixture.
Accordingly, while processes for the preparation of superconductors are known, there is a need for simple, economical processes that will enable copper oxide superconductors of a high purity. More specifically, there is a need for processes that will enable the formulation of copper oxide superconductors of a purity of 80 percent or greater. There is also a need for efficient processes for the preparation of copper oxide superconductors wherein the complex regrinding, and further pressing of pellets can be avoided. Also, there is a need for processes wherein high purity superconductors can be obtained with one heating step, and the product resulting has improved homogeneity and packing density. Furthermore, there is a need for processes for formulating superconductors wherein the pregrinding of copper oxide reactant is avoided, and wherein less energy is utilized.